Heat the oil in a large pan over medium heat. Add the onion and garlic and cook for 2-3 minutes until soft. Next, add the mushrooms and cook for another 3-4 minutes. Season with salt and pepper.
Now start adding the spinach to the pan, you will likely have to do this in batches. Cover the pan with a lid and let it wilt, repeat this step until all the spinach is in the pan. Stir well and taste for seasoning.
Make 4 indentations (‘wells’) in the spinach and break an egg in each. Cook for 5-6 minutes covered with a lid until egg whites are set.
Dress in fresh parsley and serve.